Two U.S. patents (U.S. Pat. Nos. 6,715,876 and 5,684,637) issued to inventor Johnnie E. Floyd precede this invention and attest to the effort, research, designs, and engineering pertaining to non-invasive correction of refractive errors (specifically for presbyopia) by this inventor.
A human vision limitation termed presbyopia is characterized by the inability to focus on objects nearby due to refractive errors. The ability to focus on objects far away may be diminished as well. The ratio of the far distance ability of the unaided eye divided by the near distance ability, is defined herein as the presbyopic ratio (PR). For an individual with presbyopia, PR generally decreases over time.
Correction of refractive errors can be achieved through invasive, semi-invasive, or non-invasive methods. Invasive methods include surgery to the cornea, replacement of the cornea, and/or replacement of the human internal lens with a man-made semi-rigid plastic lens. Semi-invasive methods include use of contact lenses, which are film-like flexible membranes that float on the fluids of the cornea. Contact lenses, which are usually employed for people from age 18 to 40, can provide up to three fixed focal lengths and a fixed astigmatic correction. Non-invasive methods of correcting refractive errors include traditional fixed focal length eyewear comprising frames holding a pair of fixed focal length lenses. Other non-invasive methods of correcting refractive errors include use of variable focal length eyewear employing a multitude of different technologies.
The lenses of traditional fixed focal length eyewear are typically made from relatively thick and rigid materials, namely, plastics exhibiting high impact resistance. Such lenses are generally capable of including up to three vertically stacked segments, where each segment provides corrected vision at a different focal length. Because potentially multiple segments must share the vertical height of the eyewear, each segment may have only a short height, thus requiring the user to employ both gross rapid and minute fine head rotation to place the appropriate segment between the user's eye and the object of interest and to maintain the position.
In standard industry practice, there is a repertoire of 1360 prescriptions formed from 17 cylindrical powers and 80 spherical powers (i.e., 17×80=1360) based on about 12 base curves. The ophthalmic practitioner chooses one cylindrical correction and one, two, or three spherical corrections, by testing, by interviewing the user, and/or by determining the needs of the patient in their daily life. In present practice, the anterior surfaces of the lenses contain the spherical correction(s), and the posterior surfaces contains the astigmatic (cylindrical) correction, with the axis of the cylindrical correction being oriented 90 degrees from the axis of the astigmatic error of the eye. Once manufactured these surfaces cannot be altered. After manufacture of the lenses, the surrounding lens border, called the contour, is edge ground and beveled to fit into a selected frame.
Refractive correction at three different fixed distances is universally claimed and advertised by the optical industry to be as good as can be provided. When the object of interest is located at the focal length of an optic and the person physically rotates their head to place the optic between the eye and the object, then the object will appear to the user to be in focus. But when that alignment is not possible and the distance to the object is not at the focal distance of one of the segments and accommodation is small (low P/R), the image will not be in focus, and the user and others can be put at risk. It should be appreciated that this lack of ability of a presbyope to focus has both static and dynamic aspects. The static component is the inability of the user to form sharp images at all distances. The dynamic component is the inability of the user to form sharp images continuously while the distance from an observed object to optics is changing (such as when driving an automobile). Traditional rigid lenses for advanced presbyopes do not adequately address either the static or dynamic aspects of presbyopia.